In a multiple antenna communication system, a diversity gain and receiving complexity are important standards for designing a signal transmitting apparatus. Among multiple antenna transmission methods for obtaining a maximum diversity gain, a cyclic delay diversity transmission method has been proposed. In this method, the same signal is transmitted through the same subcarrier to all transmitting antennas, and different cyclic delays are provided to the respective antennas. That is, since the different delay times are provided for the respective transmitting antennas when transmitting the signal by using the multiple antennas, frequency diversity is artificially added. Accordingly, when one channel encoding frame is transmitted through a plurality of subcarriers in a multi-carrier system such as an orthogonal frequency division multiplexing (OFDM) system, receiving quality may be improved by using the frequency diversity added by a channel decoding unit.
When cyclic delay diversity is realized at a frequency domain, τt denotes a cyclic delay value corresponding to an antenna t, fh denotes a subcarrier frequency, and a phase shifting value is given asΦ=−2 πτt·fh. 
In this case, when it is assumed that a pilot signal is transmitted by using the cyclic delay diversity transmission method, a trade-off effect may occur between a frequency diversity gain and channel estimation performance according to the cyclic delay value. That is, when the cyclic delay value increases, the frequency diversity gain increases, but the channel estimation performance is deteriorated. In addition, since the frequency diversity gain may not be obtained when the cyclic delay value is decreased to be lower than a predetermined value to increase the channel estimation performance, the purpose of using the multiple antennas may be lost. Therefore, a transmission method for simultaneously maximizing the channel estimation performance and the frequency diversity gain is highly required.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.